This project is the continuation of a broadly conceived study of the molecular and genetic biology of staphylococcal plasmids. It involves a survey of naturally-occurring plasmids with regard to markers, genetic structure, incompatibility status, and mode of replication. Highly focussed studies on representative members of the two major known classes (penicillinase and tetracycline plasmids) and of any other major classes found will involve determinations of genetic fine structure, an examination of the relationship between replication control and plasmid apportionment, and a dissection of the sequence of molecular and genetic events involved in plasmid replication. Emphasis will be placed on the identification of the roles of specific host and plasmid genes involved in plasmid replication and in the control of replication and apportionment; particular attention will be devoted to the isolation and characterization of the products of such genes and to an in vitro analysis of their actions.